X-ray generating devices are employed for example in X-ray systems for medical applications. An X-ray generating device, also known as e.g. an X-ray tube, is used to generate electromagnetic radiation, which may be used for example for medical imaging applications.
Regularly, electrons are accelerated between a cathode element and an anode element within an evacuated housing of an X-ray generating device for producing X-rays. The electrons impinge on a part of the anode element called the focal spot, thus creating electromagnetic radiation.
Anode elements may be of a static nature or may be implemented as a rotating anode element.
By employing a rotating anode, the target, i.e. the area of impingement of the electrons or the focal spot, may be considered to be a stationary area on the surface of the rotating anode disk where moving elements of the target pass a stationary electron beam. Thus, by rotating the anode, the heat load acting on the focal spot and thus the anode may be spread over a larger circular area, increasing the possible power rating of the X-ray generating device substantially.
A further factor for generating X-rays is the temperature of the focal spot. Regularly, the focal spot heats up to about 2000 to 3000° C. during operation of the X-ray generating device.
For increasing the output of X-radiation, the flux of electrons impinging on the focal spot of the anode element is to be increased.
On the other hand, the size of the focal spot may be required to be limited to achieve a desired spatial resolution of the X-ray image
With an according increase of the electron current and given the limited size of the focal spot, the temperature of the focal spot may also increase.
Thus, the combination of a pre-determined image resolution, i.e. the focal spot size and the desired X-radiation output, i.e. the power loading of the focal spot, may result in overheating the focal spot, which may result in a premature deterioration of the anode element or even in instantaneous catastrophic failure of the X-ray generating device.